1. Field of the Invention
The invention relates to an LED illumination apparatus, particularly, improvement of an LED illumination apparatus used in a vehicle.
2. Description of the Related Art
An LED is being used as a light source for indoor illumination in a vehicle by virtue of advantages such as high brightness and a long life. As a power supply in such illumination, used is a vehicle battery. The battery is also used as a power supply to another electric driving system (a wiper, a power window, an electrically sliding door, a winker, a headlight and such) in the vehicle. Recently, the vehicle battery has been also used as a power supply for electric power steering or electric driving in a hybrid vehicle.
A supply voltage from the vehicle battery to an illumination apparatus varies in accordance with an operation of an electric driving system. Especially electric power steering and electric driving in a hybrid give a load on the vehicle battery, and thereby, cause variation in battery voltage more than the variation occurring heretofore. Using the vehicle battery as a power supply for an LED under such a condition causes a change in amount of current flowing to the LED, so that the brightness is changed. Further, the LED per se is likely to be damaged due to overheat in the case that unnecessary current flows. That is to say, variation in battery voltage causes a flicker of light emitted from the LED while overvoltage on the LED causes influence upon the LED per se.
Meanwhile, heat generated by a device other than the LED is also likely to cause damage to the LED.